The research in this proposal examines the role of the endocrine and nervous systems in the regulation of maternal behavior. We recently demonstrated a central site of action for the lactogenic hormones, prolactin (PRL) and rat placental lactogens (rPLs), in the induction of maternal behavior in female rats. In a series of studies, primarily using a rat model, we propose to delineate the role of PRL and the contributions of the developing conceptus through secretion of placental lactogens in the onset and maintenance of maternal care. The central hypothesis tested is that The Onset and Maintenance of Maternal Care Are Regulated Through Common Prolactinergic (Lactogenic) Mechanisms. The first set of studies will determine whether the central behavioral actions of PRL and rPL-I are mediated by a neural PRL receptor (PRL-R). The effects of central administration of a PRL receptor antagonist in the induction of maternal are will be measured in combination with an evaluation of possible deficits in maternal care in mice in which the PRL- R has been knocked-out. The localization and expression of mRNA for the long form of the PRL-R will be characterized during pregnancy and lactation by in situ hybridization histochemistry (ISHH), and the possible regulation of the PRL-R by steroids and lactogenic hormones secreted by Rcho-1 tumors will be measured. Next, the physiological significance of placental secretions will be evaluated by push-pull perfusion of the lateral ventricle, and the biochemical specificity of placental hormone stimulation of maternal care will be assessed. Another set of experiments will address the possible interaction between PRL/rPLs and oxytocin (OXY) in order to clarify how these two important biochemical systems coordinate the rapid onset of maternal care. The effects of antagonists to OXY on PRL-stimulated maternal care will be measured to see whether PRL's actions may be mediated through the central OXY system. The final area of study will examine the consequences of reproductive experience and exposure to lactogenic hormones on neural lactogen systems that may control the maintenance and retention of maternal behavior. Specific studies examine the effects of disruptors of PRL secretion on the expression of ongoing maternal care and the possible up-regulation of the neural PRL system in experienced mothers. The results of these studies will increase our understanding of the biochemical and neural regulation of maternal care in mammals and provide a basis for evaluating the effects of endocrine and neurochemical imbalances on mother-young interactions.